This invention relates to a production process for purifying Xenon, and in particular to highly efficient procedures wherein Xenon is extracted from liquid oxygen vented from the main condenser of an air separating unit.
Xenon is contained in small quantities (i.e., 0.086 ppm) in the air and Xenon is now manufactured concurrently with Krypton from liquid oxygen that is taken from the main condenser unit of an air separating unit. There is, however, no production method presently available for manufacturing the Xenon solely from ambient air that is free from Krypton.
In a widely used commercial process for manufacturing Xenon, methane gas and trace amounts of other hydrocarbon groups (hereinafter designated as CmHn), are produced along with Xenon. As is well known, methane can be dangerous in that concentrated amounts of the gas can cause explosions.
Other methods have been proposed to prevent this problem. For example, the concentration of both Krypton and Xenon may be controlled so that the gas does not exceed a certain explosion threshold level. This can be achieved by use of a catalytic reactor for removing hydrocarbons from the gas. This type of process is reported in Fuji Techno-System Technical Report, 61-2-1, pp. 430/431, 1986. In another process, oxygen and argon are exchanged in an argon exchanging column and Krypton and Xenon are concentrated using the rectifying process as described in Tokko-Sho, 47-22937, 1972. In still another process, Krypton and Xenon are again concentrated using a rectification technique after high pressure nitrogen is exchanged for oxygen. This process is reported in Tokkai-Sho, 57-95583, 1982.
As mentioned above in connection with the widely used commercial process, liquid oxygen vented from the main condenser of an upper rectification column in the air separating unit usually contains several ppm of Xenon along with Krypton and hydrocarbons, mostly in the form of methane with some other trace elements being present. The concentration of Krypton and Xenon must be closely controlled to prevent hydrocarbon groups from exploding. This requires that (1) a multiple steps rectifying operation be employed to purify the raw Krypton and Xenon, and (2) oxygen can be exchanged for an inert gas. These additional requirements therefore increase the cost of the system and reduce its efficiency.